In High Performance Liquid Chromatography (HPLC), a sample to be analyzed is passed through a chromatography column (also referred to as separation or analytical column) to be separated into its constituent parts. The sample separation is generally performed in the separation or analytical column (also called separation column) at high pressure, such as at least 400 bar, more preferably 400-1500 bar, or even exceeding 1500 bar. The sample is pushed through the separation column by a pump. During the sample movement through the column, its individual constituents interact differently with the material packed in the column (usually granular material). In this way, different sample constituents move through the separation column at different speeds and can be separately measured. Before reaching the separation column, the sample must generally be introduced into a liquid chromatography system from a sample reservoir.
Sample retrieval and loading can be done in many ways depending on the exact application and type of analysis being done. The sample can be introduced into the system by a sample pick up means (sometimes needle or sipper) via a pressure difference. The sample can first be stored in a sample loop.
U.S. Pat. No. 8,677,808 B2 discloses, in one embodiment, a sample injection system including a vacuum source, a conduit in communication with the vacuum source, a fluid sensor configured to detect the presence of the fluid in the conduit, a sample loop in communication with the conduit; and a sipper in communication with the sample loop.
U.S. Pat. No. 8,806,922 B2 discloses a sample injector for liquid chromatography including an injection valve having a waste port, two sample loop ports, and two high-pressure ports. One high-pressure port can be connected to a pump and the other high-pressure port can be connected to a chromatography column. A sample loop is connected to one of the sample loop ports on one end and to a pump volume of a sample conveying device on the other end. A section of the sample loop can be separated to facilitate receiving a sample fluid in the sample loop. A control unit controls the injection valve and the sample conveying device. The sample injector allows a sample to be loaded into the sample loop and then pressurized to an operating pressure prior to injecting the sample into the chromatography column. The sample loop may also be isolated from the operating pressure for facilitating depressurization of the loop.
Liquid chromatography systems often comprise one or more valves for connecting the components of the system in different ways. Such valves can for example comprise “ports” and “grooves”. A component of the system can be fluidly connected to a particular port. Grooves can be used to connect two ports with each other.
In some liquid chromatography systems, a trap column is used as a means to clean, pre-filter and/or concentrate the sample before injection into the separation column. In such embodiments the sample loop may or may not be present. The trap column can be arranged upstream of the separation column. The sample is then retrieved via a sample pick up means and brought either into a sample loop and then to the trap column, or directly to the trap column. After the trap column is disconnected from the analytical flow (that is, the flow from the solvent pump to the separation column), the sample can be guided directly into the trap column (that is, it can be “trapped”) by means of another conveying device and an appropriate solvent.